The Alcubierre warp drive is an odd phenomena and object, consequence of the extreme warping of spacetime.
It was proposed by Miguel Alcubierre, a Mexican theoretical physicist in the year 1994.
Popularised in fantastical sci fi works , especially in Star Trek, the warp drive permits FASTER THAN LIGHT travel in its warm grasp.
HOW DOES IT WORK?
The warp drive comes into existence when a previously flat spacetime warps in a particular way, so that the drive works to COMPRESS and contract the spacetime in front of it, and EXPANDS the spacetime behind it, effectively enabling faster than light travel in its midst. An object in the Alcubierre warp drive would effectively be able to “surf” or ride the “waves” of movement of the drive, which will enable faster than light travel. It is very important to note that, the object in the drive is STATIONARY, and only the drive is moving.
IS GENERAL RELATIVITY FALSE?
There will not be space for controversial kicks at the basis of general relativity with the mathematics or physics of this drive. Take note that the interior of the warp will be the inertial reference frame.
1) The laws of relativity state that an object with mass cannot accelerate to light speed or anything above light speed. However, the spacecraft in the drive will not be moving, as only the drive is doing the movement.
2) Since the spacecraft is not moving by itself, it is being CARRIED along by the warp drive, time dilation and relativistic consequences like these do not apply.
3) Picture this scenario. You are in a spacecraft in an Alcubierre warp drive. You plan to go to the faraway galaxy MACS JO717. Your pilot has calculated this journey to take exactly 4 days. Your brother is observing your journey from outside the drive, standing very still in a stationary spot. As both of you are stationary relative to spacetime ( remember that you do not move by yourself in the drive ) , the process takes 3 days for both of you. No magical contortions of time is witnessed for either of you. For time dilation to come into place, you would have to be actually MOVING. And since you are in the Alcubierre warp drive that carries you along, you are stationary in that sense.Put simply, this Alcubierre metric does not violate general relativity. The movement of the warp does not dilate your time, or a stationary observer’s, as only YOUR own intrinsic movement can dilate your time.
1) There would not be a pleasant end to your journey in the warp drive. At superluminal speeds, you can imagine that deceleration would be very hard and come with a great deal of energy. The particles accumulated in the drive would be released along with high bouts of energy and deadly gamma rays when you alight at your destination.
2) If your journey is a short one ( and when you are travelling at speeds faster than light, almost all the journeys you intend to make will be short ), you might obliterate everything in your way in front of you as the energy in the drive will be too high to come to a compromise with your celestial obstacles.
3) Creating this drive would require exotic matter, or a negative energy density. And we all know, that exotic matter if created will be highly unstable and come in minuscule quantities. This would make the practical existence of such a drive very, very hard. However, Alcubierre himself has argued that the Casimir Effect could be used to stabilise and fulfil the negative energies weird devices such as the drive would need to function.
4) We still do not have a theory for Quantum Gravity, which would unite General relativity and Quantum Mechanics. The drive does follow the laws of GR, but GR as we know it is absolutely silent about quantum effects. There have been refutations arguing that Quantum Gravity would not permit time travel like this ( The Alcubierre drive effectively time travels by being faster than light). To explain why this is so, see the Chronology Protection Conjecture.
THE BEST PART
The Alcubierre warp drive does not have a limit to how fast it can travel. There is absolutely no cap on the heights of speeds it could possibly achieve.The Alcubierre warp drive also spells out T-I-M-E T-R-A-V-E-L. Faster than light implies time travel because in those reference frames, you would arrive at your destination INSTANTANEOUSLY. This would mean that the moment you depart, you arrive, no more no less time required. If you were to use a drive to go to Alpha Centauri, send a signal back to earth and then use the drive to get back, there are frames of references where you could arrive back at Earth before you even departed! When you arrive on Alpha Centauri instantly ( faster than light) there will be reference frames in which you depart to Alpha Centauri in the past. If you choose that frame, you effectively travel to earth in your past, where you would meet yourself as you are about to set up your spacecraft, getting ready for travel to Alpha Centauri. You would be in two places at once! At FTL speeds, many weird reference frames come into place, so this is possible.Also, I have to mention that the Alcubierre warp drive is MATHEMATICALLY correct as well. It follows this equation.